Jeep HU Prob....Need Help!!!

I have a 95 jeep grand cherokee laredo with the stock Infinity sound system and im installing a Pioneer DEH-P3500 cd player.....i have my harness and ive got all my wires hooked up and have the stock amp grouded too.....the unit powers on but theres a purple and white wire(both negatives) that plugged into the back of the stock cd player and i have no clue what to do with this??? If anyone here could help me i would greatly greatly appreciate it!! Thanks Alot